The present invention relates generally to medical devices for forming holes in heart chamber interior walls in percutaneous myocardial revascularization (PMR) procedures. More specifically, the present invention relates to intravascular PMR devices having expandable distal loops deployable within heart chambers.
A number of techniques are available for treating cardiovascular disease such as cardiovascular by-pass surgery, coronary angioplasty, laser angioplasty and atherectomy. These techniques are generally applied to by-pass or open lesions in coronary vessels to restore and increase blood flow to the heart muscle. In some patients, the number of lesions are so great, or the location so remote in the patient vasculature that restoring blood flow to the heart muscle is difficult. Percutaneous myocardial revascularization (PMR) has been developed as an alternative to these techniques which are directed at by-passing or removing lesions. Heart muscle may be classified as healthy, hibernating and xe2x80x9cdeadxe2x80x9d. Dead tissue is not dead but is scarred, not contracting, and no longer capable of contracting even if it were supplied adequately with blood. Hibernating tissue is not contracting muscle tissue but is capable of contracting, should it be adequately re-supplied with blood. PMR is performed by boring channels directly into the myocardium of the heart.
PMR was inspired in part by observations that reptilian hearts muscle is supplied primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive results have been demonstrated in some human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing from within a heart chamber through patent channels formed by PMR to the myocardial tissue. Suitable PMR holes have been burned by laser, cut by mechanical means, and burned by radio frequency current devices. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound.
What would be desirable is a device capable of forming relatively wide holes in the wall of a heart chamber. Such a device would be capable of forming holes having a greater width than depth and thus limit the potential of perforation of the heart wall.
The present invention pertains to a device and method for performing percutaneous myocardial revascularization (PMR). The device includes an electrode which in most embodiments has a width greater than its depth such that it can be used to form craters in the myocardium of a patient""s heart rather than channels. Craters are wounds in the myocardium of a patient""s heart which have a width greater than their depth whereas channels can be considered to have a depth greater than their width. Holes in the myocardium are volumetric removals of material. The embodiments also include a loop to limit the penetration of the electrode.
In one embodiment, a catheter assembly is provided including an elongate shaft having a proximal and a distal end and a conductor extending through the shaft. An insulator is disposed around the conductor. A conductive loop is disposed at the distal end of the shaft. The conductive loop in turn has an electrode disposed at its distal end.
The catheter shaft can include a proximal portion and a more flexible distal portion. The proximal and distal portions can be stainless steel and Nitinol hypotubes respectively.
The loop is preferably formed from Nitinol which can be heat set to expand on introduction of the loop into a chamber of a patient""s heart. The loop is preferably insulated with a material such as PTFE which can withstand high temperatures. The distal end of the loop, however, can act as an electrode if uninsulated.
The electrode can be positioned at the distal end of the loop. Preferably the electrode is substantially radiopaque such that it can readily be viewed by fluoroscopy.
In yet another embodiment, the loop is disposed proximate and proximally of the distal end of the shaft. An electrode is disposed at the distal end of the shaft. The shaft defines an elongate lumen. The lumen continues through the electrode such that contrast medium, growth factors or other drugs can be delivered to the wound created by the PMR procedure. The loop, if insulated, can act as a stop to limit the penetration of the electrode.
In yet another embodiment, the loop is retractable within the catheter shaft. In this embodiment, an elongate reciprocating shaft is disposed within a lumen defined by the catheter shaft. The reciprocating shaft is connected to at least one end of the loop, the reciprocating shaft is moveable between a first position and a second position such that in the second position, the loop has a greater transverse dimension than in the first position. In the first position, the reciprocating shaft is used to withdraw the loop into the catheter shaft lumen to reduce the transverse dimension of the loop for delivery and withdrawal from the heart.
In the method in accordance with the present invention, a catheter assembly is provided including an elongate shaft having a proximal end and a distal end. A transversely expandable conductive loop is disposed at the distal end of the shaft. An electrode is disposed on the loop. The loop is advanced to the myocardium of the patient""s heart where the transverse dimension of the loop is allowed to expand as the loop enters a chamber of the patient""s heart. The electrode is advanced to the endocardium and energized to form a crater in the myocardium. The electrode can be repeatedly advanced to the myocardium to form a plurality of craters. The electrode is preferably energized with radiofrequency energy to create an arc which ablates or removes tissue.